1. Field of the Disclosure
The present invention relates generally to control circuits that regulate an output parameter of a switched mode power converter and, more specifically, the present invention relates to control circuits that regulate a duty cycle of a diode conduction time as a proportion of a switching cycle period.
2. Background
Power converter control circuits may be used for a multitude of purposes and applications. There is a demand for control circuit functionality that can reduce the number of components outside the control circuit. This reduction in external component count enables miniaturization of the power converter to improve portability, reduces the number of design cycles required to finalize a power converter design and also improves reliability of the end product. Furthermore, reduced component count can offer energy efficiency improvements in the operation of the power converter and can reduce the power converter cost. One aspect of the power converter offering the potential for component count reduction is in simplifying or removing the external circuitry previously required to achieve output current regulation in a power converter.
In isolated flyback converters used for AC/DC power conversion, the output current is typically measured across a sense element, typically a resistor, coupled to sense the current flowing in the power supply output terminals. This sensed current is used to generate a feedback signal that is coupled to a control circuit on a primary side of the power supply that is isolated from the output of the power supply, typically employing an opto-coupler.
In non-isolated power supplies such as buck-boost converters, boost converters, SEPIC converters or Cuk converters a feedback signal representative of the power converter output current is typically generated using a sense element such as a sense resistor to generate a signal representative of an output current flowing in the output terminals of the power supply.
In both isolated and non-isolated converter configurations, a power switch is coupled to a power supply input and to an energy transfer element such that a current flows from the power supply input through the power switch and the energy transfer element when the power switch is in an ON state. The control circuit is responsive to the feedback signal to control switching of the power switch to regulate power delivered from the input to the output of the power converter.